The objective is to complete development of a catheter tip device capable of measuring instantaneous blood flow in the pulmonary artery or the aorta. The principle of operation is based upon ultrasonic detection of blood velocity and vessel cross-section area. The product of these gives instanteous volume flow. The validity of the measurement technique has been demonstrated in dogs using manual data collection and off-line processing. A high correlation (.99) was found between cardiac output measurements made using both the ultrasonic method and the dye indicator-dilution method. an automated data collection and processing system which will provide continuous measurement of stroke volume and cardiac output is near completion. We wish to accomplish several specific objectives: 1. complete the development of the automated processing system; 2. perform further testing of the system with dogs to document its accuracy, dynamic response, and safety; 3. develop several modified catheter types; and 4. evaluate the unit in a number of clinical situations. Objectives of the clinical evaluation will be initially to verify the unit's performance in humans, and then to assess its utility in diverse clinical situations.